1. Field of the Invention
This invention relates to novel polyester compositions and to sizing compositions utilizing said compositions as binders for a fibrous article such as a spun or continuous filament hydrophobic textile yarn.
2. Description of the Prior Art
Prior to the weaving operation a continuous filament polyester warp yarn is usually given a twist of about 5 to 15 turns per inch and treated with a sizing composition which binds the filaments of the yarn together so as to strengthen the yarn by rendering it more resistant to abrasive forces to which it is exposed during the subsequent weaving operation. It is less expensive to size the warp yarn than to impart a high degree of twist to the yarn in order to reduce the breaking tendency during weaving. Sizing materials, besides conferring on the yarn abrasion resistance, must have the additional properties of elasticity and flexibility with low tackiness and be characterized as easily removed subsequent to the weaving operation so as to return the yarn to its unsized state in which dyeing treatments are often performed on the woven fabric. In addition, a size solution should dry rapidly and uniformly after application to the yarn without delayed set or a tacky surface.
It is common in the Textile Industry to use as sizing materials easily removed high molecular weight synthetic and natural polymers such as polyvinyl alcohol and starch but with the advent of synthetic fibers such as polyamide and polypropylene and especially polyester fibers based upon poly(ethylene terephthalate) yarns made with synthetic fibers or those containing synthetic fibers in blends with natural fibers such as cotton are not suitably sized (because of poor adhesion thereto) with conventional natural polymer sizing materials but require a sizing material having suitable adhesion to the synthetic fibers.
Heretofore, phosphorus-containing polyester compositions have not been utilized as a sizing material either alone or in combination with other high molecular weight natural polymers such as starch. Instead, copolyesters containing the residue of a 5-sodio-sulfoisophthalic acid as disclosed in U.S. Pat. No. 3,546,008 have been used as sizing compositions on textile yarn such as poly(ethylene terephthalate). Such sizing compositions have found acceptance in the Textile Industry but difficulty has been experienced in that such sizes are difficult to remove from the fibers subsequent to the weaving operation by the usual dilute caustic solutions and, additionally, such size compositions are expensive both when used alone and even when blended with conventional sizing materials such as starch. Such sizing compositions also form such tough films on the fibers that difficulty can result during the slashing operation when the sized warp yarns are separated.
Recently, low molecular weight phosphorus-containing compositions, which are liquids at ambient temperatures and are suitable for application to metal surfaces as siccative protective coatings, have been disclosed in U.S. Pat. No. 3,415,788. These are used as aids to the inhibition of corrosion on such metal articles. Such phosphorus-containing protective coating compositions, which are soluble in hydrocarbon solvents, are prepared by reacting a benzene polycarboxylic reactant, preferably trimellitic anhydride, having at least two carboxylic groups with a polyhydroxy compound selected from the class consisting of polyhydric alcohols and polyhydric phenols, together with a phosphorus acid reactant selected from the group consisting of phosphorus pentoxide, phosphoric acid and mixtures thereof. It is also known from U.S. Pat. No. 3,396,149 (and corresponding British Pat. No. 963,966) that the preparation of mixed polyesters suitable as additives for incorporation during the melt spinning of fibers from diglycol esters of aromatic dicarboxylic acids wherein the carboxylic acid groups are 4 C atoms apart can be catalyzed by phosphoric acid. The polyesters of aliphatic glycols and the above aromatic dicarboxylic acid esters are first prepared by transesterification. The resulting ester is then condensed in the presence of added glycol and 2 to 15 percent phosphoric acid. The mixed polyester is said to have very low tensile strength and to be useful for modifying poly(ethylene terephthalate) to improve dyeability with basic dyes and dispersion dyes.
Although phosphorus-containing polyester compositions are known from the prior art, it is unexpected that the water-dispersible polyesters of the invention can be used in sizing synthetic yarn such as poly(ethylene terephthalate) yarn either used alone or in combination with starch or modified starches such as carboxylated starches. The polyester composition of this invention is prepared in the water-insoluble free acid form. In order to render such composition water-dispersible, one need only neutralize said free acid. Unexpectedly upon neutralization of the free acid form, the polyester becomes moisture sensitive as well as water-dispersible, i.e., under conditions of moderate humidity, a plasticizing effect is noted. Said phosphorus-containing polyesters are particularly suitable as size compositions because of this plasticizing effect which is particularly evident under conditions of 65-70% relative humidity and 70.degree.-75.degree. F. These polyesters are also readily removed by soaking in the usual caustic solutions utilized to remove size and clean the woven textiles subsequent to the weaving operation.